There have been tensions between the FIDE organization and top players like Carlsen since the latter have been promoting an alternative chess organization around Freestyle chess (aka Chesss960), which has slightly different rules.
I.e. this is less about "dress code enforcement" and it is more about "Carlsen is fed up with the FIDE organization in general".
One of the biggest examples of this was in his title defense against Caruana. Every game of that match had been drawn, and in the final game Magnus had a very promising position where he could squeeze with basically no risk.
Instead he offered a draw which was immediately accepted. That sent the game to rapid tie breaks where he casually butchered Caruana 3-0.